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# GATE Coaching Classes in Chandigarh

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Slides on Basics of Thermodynamics, for candidates preparing for GATE 2014 and UPSC ESE 2014.

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### GATE Coaching Classes in Chandigarh

1. 1. Thermodynamics-1 for UPSC IES and GATE 2014 Mechanical Engineering By Himanshu Vasistha
2. 2. Thermodynamics The branch of science that deals with the relations between heat and other forms of energy, and of the relationships between all forms of energy.
3. 3. System and Surroundings • A system is a ﬁnite quantity of matter or a prescribed region of space. • The actual or hypothetical envelope enclosing the system is called Boundary. • Boundary may be ﬁxed or moveable. • Everything external to the system is called Surroundings. • A System and its Surroundings together comprise a Universe.
4. 4. Types of System • Open System- In this matter and energy ﬂow in or out of the system. Most of the Engineering Systems are Open Systems. • Closed System- In this the boundary is impervious to the ﬂow of matter. A mass of gas and vapour in an engine cylinder, with a continuous boundary may be regarded as a Closed System. • Isolated System- In this the system neither exchanges energy nor matter with another system or surroundings.
5. 5. Adiabatic System vs Isolated System • An adiabatic system is one which is thermally insulated from its surroundings. • This means no heat exchange across system boundary. • Work transfer can take place across the system boundary. • If work transfer does not occur across the boundary, it becomes an ISOLATED SYSTEM.
6. 6. Macroscopic and Microscopic Points of View Thermodynamic studies are undertaken by the two different approaches:• Macroscopic approach - means Big or Total. • Microscopic approach - means small Although both approaches are different, but when applied to a system, both provide same results.
7. 7. Properties, Processes and Cycles • When properties like, volume, pressure, temperature etc. of a system have deﬁnite values, then the system is said to exist at a deﬁnite State. • Properties are the coordinates which describe the state of a system. • An operation in which one or more properties of a system changes is called change of state. • The succession of States passed during a change of state is called a process.
8. 8. • A cycle is deﬁned as a series of state changes in which the initial and ﬁnal states are identical. • Two types of properties:- Intensive properties, which are independent of the mass of the system; e.g. Pressure, Temperature etc. Extensive properties, are related to mass; e.g. Volume, Energy etc. • If mass is increased, the values of extensive properties also increase. • Speciﬁc extensive properties, i.e. Extensive properties per unit mass, are intensive properties, e.g. Speciﬁc volume etc.
9. 9. Process and Cycle
10. 10. Thermodynamic Equilibrium • Thermodynamic equilibrium exists in a system when no change of macroscopic properties is registered, if the system is isolated from its surroundings. • An isolated system always reaches in course of time a state of thermodynamic equilibrium and can never depart from it spontaneously. • If a system is in equilibrium, no spontaneous change in macroscopic property can occur. • Thermodynamic equilibrium exists when, Mechanical, Thermal and Chemical equilibrium exist simultaneously.
11. 11. Zeroth Law of Thermodynamics When a body A is in thermal equilibrium with a body B, and also separately with a body C, then B and C will be in thermal equilibrium with each other.
12. 12. • Zeroth law is the basis of temperature measurement. • There are ﬁve kinds of thermometer, each with its own thermometric property.
13. 13. Thermometer Thermometric property Constant vol. gas thermometer Pressure Constant pressure gas thermometer Volume Electrical Resistance Thermometer Resistance Thermocouple Thermal e.m.f Mercury in glass thermometer Length
14. 14. Work transfer • Work is done by a force as it acts upon a body moving in the direction of the force. • When work is done by a system, it is taken to be positive, and if work is done on a system, it is taken to be negative. • Work is one of the forms in which a system and its surroundings interact.
15. 15. Displacement work • When the piston moves, the volume changes, and the work done can be calculated as described in the ﬁgure. • The magnitude of the work done is the area under the P-V diagram. • The path shown on the P-V diagram must pass through equilibrium states; i.e. must be Quasi Static. • The integration to calculate the work done can be performed only if the process is quasi static.
16. 16. Path Function and Point Function • Area under the PV curve gives the amount of work done, so it is not a function of the end states of a process, but depends upon the path the process takes. Therefore, work is called a path function. • Thermodynamic properties are point functions, since for a given state, there is a deﬁnite value for each property. • Path Functions are called inexact or imperfect differential. • Point Functions are called exact or perfect differential.
17. 17. Work in various Quasi Static Processes PVk = constant
18. 18. Open and closed system work • The open system work is calculated by plotting it on volume axis. • The closed system work is calculated by plotting it on pressure axis.
19. 19. Zero work transfer • Work transfer is ONLY identiﬁed at the boundaries of a system. Therefore, it can be termed as a boundary phenomenon. • The expansion of a gas against vacuum is called free expansion. In this case the work done by the system is zero, as no work crosses the boundary. • This free expansion process is not a quasi static process, although the initial and end states are in equilibrium.
20. 20. Heat Transfer • It is deﬁned as a form of energy that is transferred across a boundary due to a temperature difference. • The direction of heat transfer is from a body at high temperature to a body at lower temperature. • Heat ﬂow into a system is taken to be positive, and heat ﬂow out of a system is taken to be negative. • Heat transfer is a transit, and occurs only at the boundary.
21. 21. Important points for a Heat and Work Transfer Heat and work transfer are energy interactions. The same eﬀect in a closed system can be brought about either by heat transfer or work transfer. Both transfers are boundary phenomena, and both represent energy crossing the boundaries of the system. It is wrong to say 'total heat' of a closed system as heat and work are not a property of a system. They cannot be stored in the system. Both are energies in transit Heat transfer is the energy interaction due to temperature diﬀerence only. All other energy interactions can be termed as work transfer
22. 22. Next topic:- First Law of Thermodynamics For any doubts regarding this lecture feel free to drop me an email at, himanshu.vasistha@gmail.com.